The present invention relates to mower units movable over the ground to cut grass, and particularly to a mower unit capable of mulching treatment to cut grass with mower blades, chop the grass clippings with the same blades a plurality of times to reduce the grass to small fragments, and scatter the fragments over the ground.
Such a mower unit may be the side discharge type which discharges grass clippings from one side thereof as entrained on air flows generated by the blades. As shown in FIG. 9, this mower unit includes a housing 500 having coverings extending along an inner ceiling wall thereof to lie close to and surround loci of revolution of blades 501 formed of bars. The coverings define spaces for use in the mulching treatment. Each covering includes a vertical wall 502 formed at a rear end of the mower unit with respect to a running direction: F, i.e. at the righthand side in the drawing, a ceiling potion 503 extending horizontally over the blade 501, and a connecting portion 504 bent downward from the ceiling portion 503 and bent again to extend horizontally to be connected to a forward skirt portion of the housing 500. Normally, a mower unit not designed for mulching treatment also includes a vertical wall forming part of such covering to act as a guide wall at the rear end of the housing to guide air flows generated by each blade, so that the air flows efficiently transport grass clippings. Thus, the vertical wall may be permanently fixed to the housing, while the ceiling and connecting portions are adapted to be removable from the housing. This will render the mower unit selectively usable as the side discharge type and the mulching treatment type.
If the connecting portion of each covering defining the space for mulching treatment had a small height over the ground, the horizontal surface of the connecting portion would push over upstanding grass before the grass reaches the blade. The grass pushed over and reaching an operating region of the blade would not be cut sufficiently. In conventional practice, therefore, the connecting portion is designed to have a certain height over the ground. This produces some space between the horizontal surface and the ground. However, in the course of entry of grass clippings to the space for mulching treatment to be reduced to small grass fragments, parts of the grass clippings may escape through the space between the horizontal surface and the ground. Thus, these part of the grass clippings, remaining long without being reduced to small fragments, mix into patches of grass on the ground.